In particular, the present invention relates to a razor blade having a razor blade edge.
From the prior art, razor blades have been provided. Suitably placed in a razor cartridge, they offer the ultimate function of cutting the hair.
In the past, razor blades have been provided with a substrate and a strengthening coating covering the substrate at the blade edge. The strengthening coating is generally a metal- and/or carbon-containing material, and provides enhanced strength to the razor blade edge, which in turn enhances its life expectancy.
Sometimes, the strengthening coating is further coated by a lubricating coating such as a PTFE coating.
Providing a better coating on a razor blade edge is a challenge. First of all, because the razor blade substrate edge has a very peculiar geometry, depositing a coating on it which would operate as a suitable coating by enhancing the cutting properties and strengthening the razor blade edge is very difficult.
Secondly, since razor blades are a mass consumption goods, the coating would have to be applied on a very uniform way from product to product, and at a high throughput (millions of parts per day), which requires a coating compatible with a very reliable process.
Thirdly, even if it were possible to deposit a new coating on a razor blade, measuring the improvement with respect to prior art products is also very difficult. This is because the perceived quality of shaving by test panels can be very subjective.
Hence, development of a new razor blade coating takes years of R&D work.
Nonetheless, one is still looking to improve razor blades by providing a better razor blade coating.
WO 2006/027,016 describes a razor blade coating including chromium and carbon.
Other prior art documents give endless lists of materials said to be suitable for razor blade coatings. An example of such a document is EP 1 287 953. In view of the provided long list of materials, it is likely that not all of them have been actually tried as razor blade coating components, and it is also likely that some of them would be unsuitable as razor blade coating components.
One aim, when developing a new razor blade coating, is to increase the hardness of the coating material. There are many materials harder than a mixture of chromium and carbon. One possible candidate when looking for a harder material than a mixture of chromium and carbon is titanium diboride.
It should be mentioned that there are other coated cutting tools than razor blades. These cutting tools have their own issues and structures designed to face these issues. For example, WO 2007/136,777 aims at obtaining a stable cutting edge consisting of a multilayer coating with different architectures on both sides of the blade of a rotary tool. Regarding the coating itself, it includes a specific top wear-resistant low friction anti-galling segment overlaying a bottom multilayer bondcoating cermet segment which accommodates the internal stresses in the top segment and secures the highest toughness of the entire coating system. This is a specific coating in view of specific cutting applications, where “razor blades” are mentioned as a surgical or dental instrument.
Turning back to shaver razor blades, unexpectedly, during experimentation in view of depositing a titanium- and boron-containing coating on a razor blade edge, the inventors have encountered a coating having excellent properties for a razor blade coating.